Modern operating systems and application programs for data processing devices such as, for example, computers, cell phones, gaming systems, digital video recorders, and personal digital assistants, require a pointing device for controlling the position of a cursor on a display. For computers, one successful pointing device is the “mouse”. A mouse is a handheld object that is moved over a flat surface to control the motion of a cursor on the display. The direction and distance over which the mouse is moved determines the direction and distance the cursor moves on the display. A conventional mouse provides a rigid object that a user can move with great precision.
While the mouse has provided a satisfactory solution to the pointing device problem in the desktop computer market, a similarly successful device is not available for portable and handheld devices. The Synaptics capacitive TouchPad™ and the IBM TrackPoint™ are examples of pointing devices currently used with portable and handheld devices. The TrackPoint™ is a small button typically placed in the center of a laptop computer keyboard. The button is moved in a manner analogous to a “joystick” by applying a lateral force to the top of the button with a finger.
The TouchPad™ is a blank pad, typically rectangular in shape that is placed in front of the keyboard on most laptop computers. The device senses the position of a finger on the surface of the rectangular pad relative to the edges of the pad by measuring the capacitance changes introduced by the finger on a series of electrodes beneath an insulating, low-friction material.
Unfortunately, both the TouchPad™ and the TrackPoint™ suffer from a lack of precision. The contact area of the user's finger is relatively large with respect to the overall size of the TouchPad™. Additionally, the contact area varies in size and shape with the pressure applied by the user. Therefore, to provide an accurate measurement of the finger position, the device must determine some parameter such as the center of the contact area between the finger and the pad. Such determinations are, at best, of limited precision.
Similarly, a user can only move a TrackPoint™ a small distance. Hence, the displacement of the button cannot be mapped directly into a displacement in the cursor position on a display. Instead, the button displacement controls the direction and speed of the movement of the cursor. The accuracy with which a user can position the cursor with the TrackPoint™ button is significantly less than that achieved with a conventional mouse.
In previously filed U.S. patent application Ser. No. 10/723,957 filed on Nov. 24, 2003, which is hereby incorporated by reference, an improved pointing device for handheld and portable devices is described. The pointing device utilizes a puck that moves in a defined field of motion when a user applies pressure to the puck via the user's finger. The pointing device uses a pressure sensor to sense two predetermined threshold levels. The first level is used to activate the tracking of a cursor on the display. The system changes to the track state when the amount of pressure applied to the puck exceeds the first threshold level. The second level is used to implement the “click” or select function associated with a conventional mouse. A “click” is recognized by the system when the amount of pressure applied to the puck exceeds the second threshold level.
These “touch” and “click” threshold levels require accurate calibrations in order to perform satisfactorily for a user. In practice, however, manual calibration of each individual pointing device during the manufacturing process may be difficult and impractical. Moreover, the threshold levels that are set by the manufacturer may be too sensitive for some users and not sufficiently sensitive for other users.